A common controversy about black powder is lubricant composition. Some people tell this is a bad idea to use any petroleum based products in such lube because it will produce hard, difficult to clean residues.
As far as I know, in the old days, gunners used mostly mutton tallow in order to lube their bullets, and most animal-based grease have been found an easy (available) and efficiant way for that use.
Now we can avoid the problems of stinking, liquifying or decaying animal greases, and some people tell they used petroleum jelly or lithium grease for decades with no particular problems. Unfortunetaly, other people disagree, and the exact recipes are so numerous nobody can give me rationnal and definitive answer. Looking at classic lube recipes teach us there is no consensus on such questions :
Historical Black Powder Bullet Lubricants
Composition of Extensively Used Bullet Lubricants
(E.H. Harrison, American Rifleman, Jul. 1965)
U.S. Army 1855 - 1 beeswax, 3 tallow.
U.S. Army 1861 - 8 beeswax, 1 tallow.
U.S. Army 1873 - 8 bayberry wax, 1 graphite.
U.S. Army 1880 and thereafter - Japan wax.
Sharps Rifle Co., 1878 - 1 beeswax, 2 sperm oil.
Massachusetts Arms Co. (Maynard rifle), 1890 - 1 beeswax, 3 tallow.
Marlin Firearms Co., 1891 - 1 beeswax, 4 tallow.
Smith & Wesson, 1891 - tallow.
H.M. Pope, about 1900 - 3 mutton tallow, 2 bay wax, 1 beeswax, 1 steam cylinder oil, .2 of 1 acheson graphite. The bay wax could be omitted.
Automobile door latch stick lubricant, U.S. Patent 1,920,161
(1931) - 5 paraffin wax, 3 petroleum jelly, 2 oil.
A large police department, 1962 - 1 beeswax, 1 paraffin wax, 1 cosmoline. Notes: "Cosmolene" in this context refers to dark petrolatum with no anti-corrosion additives. Refined yellow petrolatum (petroleum jelly, Vaseline) may be substituted.
Any mixture containing paraffin wax must include a plasticizer, such as petrolatum. Microcrystalline petroleum waxes may be used as-is.
The 1:3 beeswax/tallow mixture (or any composition composed mainly of tallow) is probably the most traditional choice for "primitive" shooters. The 8:1 mixture is rather stiff, and better suited to conicals, paper cartridges, and the like. For paper-patched bullets, I'd be inclined to try the Sharps formula, substituting Dexron II/III automatic transmission fluid for the sperm oil.
Could someone explain or quote some good source explaining if and why petroleum based lubricant will produce such disagreement with black powder?